The solvent contribution to nucleic acid stacking is being studied. Model systems include: (1) planar dyes, (2) single strand nucleic acids, (3) double strand nucleic acids, and (4) double helical oligonucleotides with non-basepaired ends. The rate constants for stacking are being measured with a laser temperature-jump apparatus. Melting curves of oligomers are being used to obtain the thermodynamics of stacking as a functon of solvent. The dependence of conformation on solvent is being studied by circular dichroism and fluorescence detected circular dichroism. The latter method is being extended to systems with polarized fluorescence. Finally, the relevance of these results to protein-nucleic and interactions is being investigated.